I would suggest that you don't put this on FB. You can always note how well he is doing in school and mention in general terms that he is doing advanced work. Being gifted indeed as someone mentioned brings along its own challenges and in today's digital word of cyber bullying please be careful not to give other kids an additional opportunity to bully or negatively single out your child. Some things are best kept private in order to protect your child today and most significantly in the future.
In the meantime enjoy your child's accelerated intellectual path in life and help him adjust socially with his extraordinary gift. Be sure to keep him intellectually stimulated and also offer positive non-academic challenges into his life. Is it not wonderful the possibilities that might exist for him? Best wishes always and enjoy your gifted child.